Purple Shore Crab

Scientific name:  Hemigrapsus nudus

Author: George Sleen

Photos: George Sleen and D. Young

Length: Male adult purple shore crabs typically grow to a width of 2.2 inches while females will grow to around 1.3 inches across

Identification:  The purple shore crab has a few distinct physical features:

  • Coloration: Like the name suggests, purple shore crabs are usually a dark red or purple in color, but there is also a green morph that has no spots on its claws.
  • Carapace: The carapace (the shell of the crab) is square in shape, and has a distinct hump on the back. It is widest at the level of the eyes and tapers towards the back.
  • Claws: The claws of the purple shore crab have distinct spots on their claws that help to differentiate them from the Yellow Shore Crab (Hemigrapsus oregonensis). They will also have a white tip on their legs and claws.

The green morph of the Purple Shore Crab

The purple shore crab shares many similarities with other shore crabs from the genus Hemigrapsus, especially the Yellow Shore Crab (Hemigrapsus oregonensis), which is why the spots on the crab’s claws are important to look at.  

Habitat:  The purple shore crab is found in the intertidal zone along the Pacific coast of North America. It inhabits rocky shores, tide pools, and sandy or muddy areas in the intertidal zone.  They are active during the day and hide during the night, often in crevices or under rocks. They can burrow in the sand or mud to stay moist during low tide.

Prey:  The purple shore crab is an opportunistic feeder, which means that it will consume a wide variety of organisms. They typically feed during low tide. Some of its known prey include:

  • Algae: Purple shore crabs consume various types of algae, including kelp and seaweed.
  • Barnacles: Purple shore crabs will feed on barnacles, both as adults and as juveniles.
  • Mollusks: Purple shore crabs are known to consume various types of mollusks, including mussels and snails.
  • Other crustaceans: Purple shore crabs can consume other crustaceans, such as small crabs and shrimp.
  • Organic debris: Purple shore crabs also consume detritus and other organic matter, such as dead fish and seaweed.

The diet of the Purple Shore crab may vary depending on the location and the availability of food.

The common purple form or the Purple Shore Crab beside the rarer green morph of the species.

It is quite common to find the molts of Purple Shore Crabs on the beach as in the photo above.  Though dead crabs may look similar, they are more likely the molts.  When the molts dry in the summer sun they turn a light red-orange colour.  You can really see the distinct red spots on the claws that are used to identify this species.

Predators:  The purple shore crab is an important prey item for many organisms and is known to have several natural predators, including:

  • Birds: Birds such as gulls, crows and other shorebirds feed on purple shore crabs, especially during the low tide when they are exposed.
  • Fish: Many types of fish will feed on purple shore crabs, as well as some other types of crustaceans.
  • Other crabs: Purple shore crabs are known to be preyed upon by other crabs, such as dungeness and red rock crabs.
  • Sea star: sea stars will feed on purple shore crabs, as well as other invertebrates if they get a chance.

Predation of the Purple Shore crab may vary depending on the location and the availability of other prey. Adult crabs have a better chance to survive from predation as they have a more developed carapace and better developed claws. Juvenile crabs are more vulnerable to predation.

Life Cycle: ​​  The Purple Shore Crab has a typical crustacean life cycle:

  • Eggs: Female Purple Shore Crabs carry the eggs in their abdominal flap, which are then fertilized by males and carried on the female’s abdomen.
  • Larvae: The eggs hatch into planktonic larvae, which go through several developmental stages, known as zoea, before going to the megalopa stage.
  • Juveniles: The megalopa stage settles on the bottom and begins to resemble an adult crab, but is still small and lacks adult characteristics.
  • Adults: The juvenile crabs continue to grow and molt, eventually reaching maturity and reproducing.

A female Purple Shore Crab carrying her eggs below her abdomen.


Brietzke, C., Fretwell, K., & Starzomski, B. (2016). Purple shore crab • Hemigrapsus nudus. Biodiversity of the Central Coast. Retrieved January 25, 2023, from https://www.centralcoastbiodiversity.org/purple-shore-crab-bull-hemigrapsus-nudus.html

Cowles, D. (2005). Hemigrapsus nudus. Hemigrapsus nudus (Dana, 1851). Retrieved January 25, 2023, from https://inverts.wallawalla.edu/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Brachyura/Family_Grapsidae/Hemigrapsus_nudus.html

Gohiking. (n.d.). Purple Shore Crab, Vancouver Island, BC. Gohiking.ca. Retrieved January 18, 2023, from https://gohiking.ca/animals/fish/crustaceans/purple-shore-crab/

Seattle Aquarium. (n.d.). Purple shore crabs. Seattle Aquarium. Retrieved January 18, 2023, from https://www.seattleaquarium.org/animals/purple-shore-crabs

Common name: Western Sea Roach, Rock louse

Scientific name: Ligia occidentalis

Size: To 2.5cm (1″)

Author: Aina Saitoh

Photos: D. Young

The Western Sea Roach is an isopod within the subphylum Crustacea and phylum Arthropoda. Their bodies are flat and vary in colour including grey, yellow and brown. Their body is separated into seven main parts and their uropods (the long structures at their hind end) are quite long relative to the closely related species Ligia pallasi. They have special cells, chromatophores, which allow them to change their color to camouflage into the background.  They are generally lighter in colour during the night and then darken during the day time.  They live around the sea in part because they need to keep their gills, located near their posterior end, hydrated in order to breathe. However, they can drown if they are submerged so are considered to be largely a terrestrial organism.  They are very fast and will quickly hide in crevices along the rocky shoreline.  They are found above the water line up to the high tide line.  They are often active at night when they feed on microscopic algae (phytoplankton) and, as an omnivore, scavenge for a diversity of other food sources as well.

This rocky shoreline, located on a southern Gulf Island in British Columbia, is a typical habitat of the Western Sea Roach.  Many sea roaches, including the one in the photos above, were scurrying along these rocks on a warm summer day.


A Brief Encounter with a Western Sea Roach. (n.d.). Nature Chronicles. Retrieved January 23, 2023, from https://naturechronicles.wordpress.com/western-sea-roach/

Cowles, D. (n.d.). Ligia occidentalis. Retrieved January 23, 2023, from https://inverts.wallawalla.edu/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Peracarida/Isopoda/Oniscoidea/Family_Ligiidae/Ligia_occidentalis.html

General Format – Purdue OWL® – Purdue University. (n.d.). Purdue OWL. Retrieved January 23, 2023, from https://owl.purdue.edu/owl/research_and_citation/apa_style/apa_formatting_and_style_guide/general_format.html

Species Ligia occidentalis – Western Seaslater. (2010, May 5). BugGuide.Net. Retrieved January 23, 2023, from https://bugguide.net/node/view/392515


Duane, S. J. (2019). The New Beachcomber’s Guide to the Pacific Northwest. Harbor Publishing.

Northern Kelp Crab

Common name: Northern Kelp Crab, Shield-Backed Kelp Crab

Scientific name: Pugettia producta 

Size range: Carapace 7.8-9.3 cm across, with differing appendage sizes 

Author: Ruby Wallace

Photography: Thank you to Andy Murch for permission to use his photos on our page!

Identifying Features:   Northern Kelp Crab are part of a superfamily of crabs called the Majoidea (spider crabs) and are most easily identified by their shield-shaped carapace and 4 long, hairless walking legs. Telling the difference between males and females is hard, but generally male Northern Kelp Crabs have a bigger carapace, averaging at about 9.3 cm across, and females about 7.8 cm across.  The second pair of their legs is the strongest and longest, being up to 1 ½ times their body length. Adult Northern Kelp Crabs are brown or red in colour, while juveniles are greenish-yellow. Unlike other crabs such as the Graceful Kelp Crab (Pugettia gracilis) who also have a shield-like carapace, the carapace of the Northern Kelp Crab is uniquely smooth and hard. The underside of the Northern Kelp Crab is usually red and/or yellow. You can sometimes tell when a Northern Kelp Crab hasn’t molted in awhile if their body is covered in the white and grey, mold-like appearance of invasive colonial tunicates. A Northern Kelp Crab after its terminal molt will often be covered in barnacles.

Habitat:  Northern Kelp Crabs live primarily along the West Coast of North America, from Southern Alaska to Northern Mexico. They occupy kelp beds and forests and are especially common in swaths of Bull Kelp. Juveniles have been spotted in tide pools or smaller beds of Rockweed or Surf grass. Adults can be found anywhere from intertidal zones, up to 73 meters down. At times, they are seen at wharf pilings. 

Food (Prey):   Generally, the Northern Kelp Crab is a nocturnal feeder. Most of the year, it is a herbivore and feeds on Kelps, seaweeds such as the red algae primarily in the spring and summer. One unique behaviour of the Northern Kelp Crab is that it does not camouflage on purpose like the Graceful Decorator Crab (Oregonia gracilis) or the Graceful Kelp Crab (Pugettia gracilis) does by covering their carapace in kelp. This is probably because the Northern Kelp Crab is faster and larger and has less need for strategic camouflage. The only time the Northern Kelp Crab is observed exhibiting this behaviour is to hold onto their food through the day – similar to a backpack – and only taking bites when needed, while freeing up the pincers for defense and communication. During the Winter months, when the kelp beds and algae have decreased in volume, Northern Kelp Crabs turn to a mainly animal-based diet of barnacles, bivalves, hydroids, and bryozoans. 

Predators:   Sea otters are the most common predator of the Northern Kelp Crab, as they are in heavy abundance in most kelp forests. Other predators include the Staghorn Sculpin, various gulls, and cabezons. Oftentimes the Zoea larvae of Northern Kelp Crabs are eaten by Velella velella. Parasites are also an issue for Northern Kelp Crabs, one such parasite; the Heterosaccus californicus causes the Northern Kelp Crab to become sluggish, and destroys the male reproductive organs. In turn, many males become hermaphroditic and develop female reproductive organs. One defense against predators that the Northern Kelp Crab possesses is its speed and relatively aggressive nature. Its pincers and hard carapace also offer some protection.  

Life Cycle:   Adult Northern Kelp Crabs migrate to deeper waters in the Fall to mate. Once the eggs of a female have been fertilized, they are stored in her abdombale sac, also called an pron. Females can be seen throughout the seasons carrying eggs. One clutch from a female can contain anywhere from 34,000 to 84,000 eggs. At first, the eggs are bright orange, then become red, and finally, before hatching, the eggs will become grey and purple. This process can take anywhere from 2 weeks to a month. After being hatched, the zoea larvae will drift away and develop into megalopae, and then into juveniles where they take on the green/yellow colouration. Embryonic development of Northern Kelp Crabs varies wildly but usually the entire process takes about 1 year. 

 Fun Facts: 

  • Like most Brachyura, the Northern Kelp Crabs cannot osmoregulate (cannot regulate internal balance of disolvants and fluid relative to surroundings) and therefore cannot survive in brackish water 
  • Though not considered a popular crab for commercial fishing, the taste of a Northern Kelp Crab has been described as “sweet” and the texture “stringy” 


Cowels, D. (2005) Pugettia producta (Randall, 1839). Invertebrates of the Salish Sea. Retrieved January, 29, 2022 from https://inverts.wallawalla.edu/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Brachyura/Family_Majidae/Pugettia_producta.html

NorCal. (Dec, 2005). Are Kelp Crabs Edible?. NorCal Kayak Anglers. Retrieved January, 29, 2022 from http://www.norcalkayakanglers.com/index.php?topic=42781.0#:~:text=IF%20these%20are%20the%20red,any%20crab%20I’ve%20eaten.

SanctuarySimon.org. (2002). Kelp Crab Pugettia producta. Explore California Sanctuaries. Retrieved January, 29, 2022 from https://sanctuarysimon.org/dbtools/species-database/species-info-ajax.php?sID=169#:~:text=Adult%20Pugettia%20producta%20lives%20mostly,about%2073%20meters%20in%20depth.

University of Puget Sound. (2022). Kelp Crab (Pugettia producta). Slater Museum of Natural History. Retrieved January 29, 2022 from https://www2.pugetsound.edu/academics/academic-resources/slater-museum/exhibits/marine-panel/kelp-crab/

Taylor Coastal Shrimp

Author: Rubin Johnston

Scientific Name: Heptacarpus taylori

Size Range: The average length of adults is around 28mm (1.1 in)

Identifying Features: Taylor Coastal Shrimp have a variety of colours, including red, brown, black, and green. Two things that make this species stand out are the arched back, and the distinct white patches on the top of its head and body.  These patches may appear as separate patches or as a single large white patch similar to the one shown in the photos. 

This species is commonly found near the shore, often in tidepools.  They are omnivorous and will eat plants, plankton, and scavenge on dead animals.  They are near the bottom of the food chain, so they have many predators, like crabs, sea urchins, starfish, and seabirds.  Similar to other shrimp, during reproduction the male transfers a packet of sperm called a spermatophore to a pouch on the female’s abdomen.   The female will produce eggs that she keeps in the same pouch until hatching. When the eggs hatch, the larvae over multiple weeks drift along in the current as nauplius and then metamorphose into zoea.  The zoea larvae then develop into juvenile shrimp which can swim to food and usually end up by the shore, where they live and mate as adults.


Jensen, G. C. (2014). Genus Heptacarpus. In Crabs and shrimps of the Pacific Coast: A guide to shallow-water decapods from southeastern Alaska to the Mexican border (pp. 132–133). essay, MolaMarine.

Phronima Sedentaria

Scientific Name:  Phronima sedentaria

Author:  Eduarda Ferro Braga Laurindo Correia

Size Range:  These are tiny creatures with sizes ranging from 1.2-4.2 cm (~0.5 to 1.7 inches). 

Life Expectancy:  They live around one year. 

Identifying Features:  Phronima sedentaria can be distiguished by its very large head which is composed of two very large transparent compound eyes.  It also has two lateral compound eyes and 4 distinct red retinae.  The internal anatomy of these creatures is reasonably similar to that of other amphipods, but there are some key characteristics that differentiate them. As an example, their foregut is reduced and surrounded by a midgut chamber. Their brain is circumesophageal with four pairs of major nerves, that lead to their 4 compound eyes and to their ventral nerve cord and antennules. This organism has numerous specialized legs including two large claws, as well as a tail with 3 pairs of swimmerets (pleopods) it uses for swimming.  They also have pigmented-cells called chromatophores that are responsible for camouflage; these cells contract to give the organism a transparent appearance so it will be unseen or mistaken as harmless plankton by the prey. 

Mating Behaviour:  Males use their antennae to find potential mating partners in response to the release of pheromones by the females. The male will then ride or hold onto the female until she is ready to molt, the male will then push the sperm into the marsupium and release the female when it is complete. After a couple of hours, the female will release her eggs into the marsupium for fertilization.

Habitat:  They are usually found in temperate and tropical waters around the world and can live anywhere between the surface and deep water. 

Food:  Their feeding behaviours depend on the consistency of the food being eaten. The specialized legs called pereiopods are used during feeding to pick and pull prey with soft bodies toward their mouths, where the mouthparts are responsible for removing smaller pieces and directing them to the esophagus. When the tissue of the prey is tough other pereiopods work to keep it across the mouth cone area while the mandible breaks it down into smaller pieces. If the tissue is fluid-like, the contents will be sucked into the foregut with the help of the muscles of the esophagus and gut. One example of food they might ingest is zooplankton.

Predators:  Fish are some of the most prominent predators.

The photo above shows the adult female that ventured outside of the salp containing her juvenile offspring within.  

Life Cycle:  Phronima sedentaria make their homes in hallowed salps. They attack their victims by slicing them open with their claws, eating the soft tissue of the prey and then using the barrel-like leftovers as a gelatinous home. Females will lay their eggs in this barrel, which also provides protection from predators and space for food storage. These eggs will hatch inside of the barrel, and it will, later on, serve as food for the young amphipods. These young amphipods can be seen swimming around the barrel.  At times both the adult and juveniles in our lab could be seen leaving the barrel and re-entering it. 

Two juveniles inside the salp with their mother’s head above.

The visual system of Phronima sedentaria has been described as extraordinary and has often been studied.  The two median compound eyes are unusual in their size with crystalline cones reaching up to 5mm in length.  The structure is thought to give Phronima resolution under very low light levels while also  being transparent, a benefit when avoiding detection by predators.

The illustration on the right is adapted from Ball, E. E. 1977.  Fine structure of the compound eyes of the midwater amphipod Phronima in relation to behavior and habitat.  Tissue & Cell 1977 9 (3) 521-536

Video Production: Eduarda Ferro Braga Laurindo Correia

Photos and Video:  Misha Young and David Young

Special thanks for Misha for finding the specimen off the shores of Victoria.


Amphipod: Salp Invader. (2018, May 18). Retrieved January 25, 2021, from https://ocean.si.edu/ocean-life/invertebrates/amphipod-salp-invader

Ball, E. E. (1977). Fine structure of the compound eyes of the midwater amphipod Phronima in relation to behavior and habitat. Tissue and Cell, 9(3), 521-536. doi:10.1016/0040-8166(77)90010-6

Diebel, Carol. (1988, January 1). Observations on the Anatomy and Behavior of Phronima Sedentaria (Forskal) (Amphipoda: Hyperiidea). Journal of Crustacean Biology, 8(1). Retrieved January 25, 2021, from https://academic.oup.com/jcb/article-abstract/8/1/79/2327686?redirectedFrom=fulltext

Phronima sedentaria. (n.d.). Retrieved January 25, 2021, from http://sio-legacy.ucsd.edu/zooplanktonguide/species/phronima-sedentaria

Phronima sedentaria. (n.d.). Retrieved January 25, 2021, from https://www.sealifebase.ca/summary/Phronima-sedentaria.html

Van Couwelaar, M. (n.d.). Zooplankton and Micronekton of the North Sea. Retrieved January 25, 2021, from http://species-identification.org/species.php?species_group=zmns&menuentry=soorten&id=370&tab=beschrijving

Young, L. (n.d.). A Plankton Species Straight Out Of A Horror Movie. Retrieved January 25, 2021, from https://www.sciencefriday.com/articles/monster-in-a-barrel-and-other-haunting-ocean-drifters/

Gammarid Amphipod

Common Names: Amphipod

Author and Photographer:  Samantha O’Keefe

February 19, 2013 Plankton Tow – Cadboro Bay

Umbrella Crab

Authors: Fai &Vivian

Scientific name:   Cryptolithodes sitchensis

Common name: Umbrella crab, Sitka crab or Turtle Crab    

Size Range:  5 – 10 cm (2.0 – 3.9in)

Identifying Features

The Umbrella Crab is a species of Lithodid crustacean native to coastal regions of the northeastern Pacific Ocean, ranging from Sitka, Alaska to Point Loma, California. They have a half-moon shaped carapace extending over all of their eight walking legs and two chelipeds. The carapace can be 5–10 cm (2.0–3.9 in) at the adult stage and has scalloped edges. This carapace ranges from neutral sandy colors to bright oranges, reds, and purples.



Umbrella Crabs can be found on bedrock. They live within 18 m (59 ft.) of the intertidal zone along the exposed coasts of the Pacific Ocean. Intertidal species of Lithodidae prefer habitats of cooler temperatures ranging from 0–25 °C (32–77 °F).



Umbrella Crabs feed mostly on algae and tiny sessile organisms.



The major predators are otters, sea birds, octopuses and other marine animals. They have a few defenses to avoid being eaten. Their shell is their first layer of defense. While their shell may not deter the aforementioned predators, they do ward off animals that cannot crush or open them. When threatened. The best defense is the anemone: it catches bits of food off of the crab’s shell and, in return, it defends the crab from predators by stinging animals with it’s poisonous tentacles.


Life cycle

The Umbrella Crab reproduces sexually, using the molting cycle. There are six stages in the development of this crab similar to other crabs: Eggs, Prezoea, Zoea, Megalops, Juvenile Instar and Adult Crab.



Its distinctive shell allows it to camouflage itself into its surroundings. It is often mistaken for an old clam shell or patch or coralline algae.

Photographs by D. Young


Andy Lamb and Bernard P. Hanby (2008). Marine Life of the Pacific Northwest:  A photographic
encyclopedia. Habour publishing.

Andrew .Lets do some zoology!.Retrieved December 10,2014 from: http://astronomy-to-zoology.tumblr.com/post/81502745300/umbrella-crab-cryptolithodes-sitchensis-also

Dave Cowles (2005). Cryptolithodes sitchensis Brandt, 1853. Retrieved December 4, 2014 from http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Anomura/Family_Lithodidae/Cryptolithodes_sitchensis.html

Lester B. Pearson College (2003).  Cryptolithodes sitchensis. The Race Rocks Taxonomy. Retrieved December 4, 2014  from http://www.racerocks.com/racerock/eco/taxalab/bio2003/ cryptolithode ss /crypt olithodess.htm

Nobert (2011). Weird, unique and commercially important King crab Species. ABCs of animal world.  Retrieved December 10, 2014 from http://abcsofanimalworld.blogspot.com/2011/10/weird-unique-and-commercially-important.html.


Author:  Conor Graff

North Pacific Krill

By Conor Graff

Common Name: North Pacific Krill

Scientific Name: Euphausia pacifica

Size range: Between 16 and 25mm

Identifying features:

The North Pacific Krill is an ocean-based crustacean that can grow up to 25mm in length (this is a bit of a stretch, however; most average around 16mm). The word Euphausia is Latin for ‘brightly shining’, and indeed, these small invertebrates are noted for what appears to be a bioluminescent characteristic throughout their species. North Pacific Krill have large black eyes and large abdomens, and closer inspection reveals what appear to be gills formed around their legs, and scales on their antennae (these scales are very large and used to protect their antennae from damage).


The North Pacific Krill live, as their name would suggest, on the ocean of the same name. This stretch in habitat runs from the southernmost coasts of the US all the way to Japan, and due to their instincts to band into close ‘clouds’ of themselves, they can cover large areas as a quasi-community without having to move from one place to another. However, the accumulation of these krill is anything but organized; while krill can accumulate into these areas of themselves, they usually form these clusters in areas that would be the most hospitable. The gist is that these krill can be found in very large quantities around the stretch that is their habitat, while other areas are completely barren of krill.

Krill tend to dwell in the ocean’s “twilight zone” (the area between the ‘surface zone’ and the ‘bottom zone’), wherein they can stay out of the reach of most surface zone-dwelling predators. Krill swim to the surface zone during the night, where, under cover of darkness, they can find and feast on their food source, phytoplankton.


As mentioned above, krill feed mostly on phytoplankton (“plant plankton”), making them herbivorous. They feed via a complicated system in their mouthparts wherein the phytoplankton is filtered out of the water into the krill’s jaws.

Krill do not feed exclusively on phytoplankton; many are omnivores who feed of animal plankton (zooplankton). As mentioned before, Krill only come out at night to feed (all the better in escaping from hungry predators).


Krill are perhaps the richest form of protein in the entire ocean, which may be why a certain surface-dwelling species (humans) have discovered and started harvesting them.

They tend to be a primary diet of baleen whales and a number of fish (notably salmon); however, humanity has begun to take an interest in these small creatures. In BC, krill are fished out in large quantities in order to feed aquariums, fish farms, and ourselves; Japan is also immensely interested. Those who have tried krill tend to say it has no taste when fresh and raw; however a bitter, powerful flavor is created from krill that is dried out in the sun or frozen.

Life Cycle:

Krill reproduction starts out in a familiar way to nearly every living creature: that with the release of sperm. Upon receiving the male Krill’s sperm, females store the semen in their bodies and fertilize them, and proceed to release the eggs that come out of this union. A female can release up to 20 000 eggs at a time in clusters with intervals in between.  The eggs are laid several hundred meters in the twilight zone, where the larvae can safely hatch without being attacked by most day-dwelling creatures. Upon hatching, krill larvae feed of the nutrients given by the egg yolk. Larvae soon develop through many stages in order to finally reach their adulthood.

Read more

Spot Prawn

Authors:  Aidan McReynolds and Zack Schmit

Common Names: Spot Prawn, Pacific Prawn

Scientific Name: Pandalus platyceros

Size Range: 15 to 22 cm in length at maturity

Identifying Features

Spot prawn are usually 15-22 cm in length when fully matured, making them larger than most shrimp. Two pairs of white spots on the abdomen identify them. They are of a pink or red-brown colour and have white lines on their carapace. They have an upturned rostrum. Their front two legs don’t have pincers but the second ones have small ones.


Spot prawn are found in the intertidal region, to about 485m beneath the sea level. They range from the northern parts of the Alaskan coast, to southern California, and are also found along the Korea Strait, and in the Sea of Japan.  Their main location along the seashore is on jagged rock faces and sheer underwater cliffs. They move to shallower waters at night to hunt.


Spot Prawn catch thier prey with their long legs and often hunt at night. In general, prawns and shrimp that are less than 1 cm in length eat plankton. When they are larger they will eat small shrimp, small shellfish and worms. They also eat dead crabs and fish. Prawns and shrimp are not very selective about what they eat.


Predators of Spot Prawns, during the early larval stage, are mostly jellyfish and plankton feeding fish such as herring. Animals that prey on adult Spot Prawns include fish (sculpin, salmon and flatfish), seagulls, and crabs. Defences that shrimp and prawns employ to avoid being eaten include fast swimming, quick withdrawal to underwater crevices, and colour camouflage. Adults Spot Prawn hide in eel grass to a avoid predators. Young hide under other algaes such as sea colander kelp.


A female Spot Prawn will produce somewhere around 3,000 eggs, which will then become attached to tiny hairs on her bottom side, under her tail. Depending on the time of year, the eggs will be incubated for anywhere between 4 weeks and 3 months. The eggs will then hatch and begin to float around in the water, eating plankton. After they reach one centimetre in size, they will begin their life on the bottom of the sea. Baby Spot Prawn have a green tint to them. After one year, they will have matured fully into an adult. They then spend two years as male, and then undergo a process changing their sex to female. A male will change his sex early, if the male to female ratio is imbalanced.


With 2450 metric tonnes harvested annually Spot Prawns are BC’s largest shrimp/prawn industry. Fresh prawn are available starting in May for 6 to 8 weeks. According to the David Suzuki Foundation’s Seachoice Programme, the Vancouver Aquarium’s Ocean Wise programme and the Monterey Bay Aquarium’s Seafood Watch; the spot prawn industry is sustainable.

Photos by Aidan McReynolds and Zack Schmit


Barrows, Edward M. (2001). Animal behavior desk reference: a dictionary of animal behavior, ecology, and evolution (2nd ed.). Boca Raton, Fla: CRC Press. p. 317. ISBN 0-8493-2005-4. OCLC 299866547.

Butler, T. H.(1980) Shrimp of the Pacific Coast of Canada. Ottawa, Ontartio, k1A 0S9: Canadian Government Publishing Center.

Harbo, Rick M.(2011) Whelks to Whales. Coastal marine life of the pacific north west. Madeira Park, BC, V0N 2H0: Harbour publishing co, Ltd.

Jensen, Gregory C.(1957) Pacific Coast Crabs and Shrimps. Montery CA 93940. Sea Challengers

Lamb, Andy and Hanbe, Bernard P. (2005) Marine Life of the Pacific Northwest. a photographic encyclopedia of invertabrates, seaweeds and selected fishes. Madeira Park, BC, V0N 2H0: Harbour publishing co, Ltd.

Rockweed Isopod

Authors: Emma Hornell and Lilly Powell

Common Names: Rockweed Isopod, Pickle Bug, or Kelp Isopod

Scientific Name: Idotea wosnesenskii

Size Range: 4cm (1.6 inches) in Length

Identifying features

Rockweed Isopods are shrimp-like creatures with 7 pairs of clawed-tipped legs. The males are slightly larger than the females, are paler, and have thicker legs. The colour of individuals can vary from green, brown, to black.  It is dependent on their diet and can help them camouflage into their environment. For example some individuals found in coralline algae are very dark red in colour while those living amongst Rockweed are a dark olive green. Their bodies are segmented and flattened from top-to-bottom.


Rockweed Isopods can be found along the Pacific Coast from California to Alaska. They live in the intertidal zone and can be found under rocks or clinging to the holdfasts, stalks or blades of seaweed such as the Rockweed (Fucus gardneri).  They are also sometimes found in mussel beds.


Rockweed Isopods are scavengers, surviving mainly on marine plants, algae and algal detritus, and occasionally the eggs of molluscs such as the Emarginate Dog Winkle (Nucella emarginata).


Rockweed Isopods have a myriad of different predators that likely include foraging shore birds and fish.


To protect itself from predators the Rockweed Isopod relies on camouflage and its ability to hold tightly to rocks and seaweed.  Though some marine isopods are able to roll up into a small ball like their terrestrial relatives the Rockweed Isopod is not so flexible. The principally nocturnal creature, however, is a gifted swimmer, using paddle-like appendages on its abdomen to maneuver itself around.

Life cycles

The average lifespan of a Rockweed Isopod is three to four years.


Rockweed Isopods reproduce around spring when the male fertilizes the female. The female Isopod holds her young in body pockets while they develop for three to four weeks, finally hatching as miniature adults.

Fun Fact:

Idotea (Pentidotea) wosnesenskii was Named after Russian biologist Ilya G. Voznesenskii.

Original video by Aries

Video editing by Emma Hornell and Lilly Powell


Cowles, Dave. (2006). Idotea wosnessenskii. WWU: On Campus. Retrieved May 7th 2013 fromhttp://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Peracarida/Isopoda/Valvifera/Family-Idoteidae/Idotea_wosnessenskii.html

Houck, Becky; Fergusson-Kolmes, Linda; Kolmes, Steven; Lang, Terra. (n.d). Final Report on Intertidal Invertebrates in Tillamook Bay – A Report to the Tillamook Bay National Estuary Project. Department of Biology, University of Portland. Retrieved May 9th 2013 fromhttps://nrimp.dfw.state.or.us/web%20stores/data%20libraries/files/Watershed%20Councils/Watershed%20Councils_440_DOC_InvertebrateFaunaOfTillamookBay.pdf

Jamison, David. W. Kelp Isopod. Pugetsoundsealife.com. Retrieved May 7th 2013 fromhttp://www.pugetsoundsealife.com/puget_sound_sea_life/Kelp_Isopod.html

Pentidotea wosnesenskii. (2013, April 13). In Wikipedia, The Free Encyclopedia. Retrieved May 9th, 2013, from http://en.wikipedia.org/w/index.php?title=Pentidotea_wosnesenskii&oldid=550200397

Vancouver Sun. (May 2nd 2009). Urban critter: Rockweed isopod. canada.com | Join the discussion. Retrieved May 7th 2013 fromhttp://www.canada.com/vancouversun/news/westcoastnews/story.html?id=a16723b7-293d-4080-ab7b-671c4ddbc935